Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2002-01-11
2003-06-10
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S108000
Reexamination Certificate
active
06577173
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to an inductive load driving circuit for supplying current to an inductive load. In particular, the present invention pertains to a technology for preventing occurrence of surge voltage caused by the counterelectromotive force of the inductive load.
BACKGROUND OF THE INVENTION
Conventionally, an inductive load supply circuit has been used widely to supply current to an inductive load, such as the winding in a motor.
Its operation theory will be explained using inductive load driving circuit
101
shown in FIG.
6
.
Said inductive load driving circuit
101
has an output transistor
105
made of an n-channel MOSFET, a transistor control circuit
118
that operates said output transistor
105
, and an inverter
112
that is inserted between the output terminal of transistor control circuit
118
and the gate terminal of output transistor
105
to invert the output signal of transistor control circuit
118
and then send it to the gate terminal.
Symbol
121
represents the output terminal on the high potential side of said inductive load driving circuit
101
, while symbol
122
represents the output terminal on the low potential side. A positive voltage output from DC voltage source
123
is applied to the high-potential output terminal
121
. The drain terminal of output transistor
105
is connected to the low-potential output terminal
122
.
A load
126
is connected between high-potential output terminal
121
and low-potential output terminal
122
. When output transistor
105
is turned on and low-potential output terminal
122
is grounded, a current is supplied from DC voltage source
123
to load
126
.
When output transistor
105
is converted from on to off, the current flowing to load
126
is stopped.
Since the current flowing to load
126
can be controlled with the on and off state of output transistor
105
as described above, the magnitude of the average current flowing to load
126
can be maintained at a constant level by keeping the on period and off period of output transistor
105
as well as their ratio constant.
However, since load
126
is inductive, an induced electromotive force with positive polarity is generated at low-potential output terminal
122
when output transistor
105
is converted from the off state to the on state.
FIG. 7
shows the variation in the voltage of low-potential output terminal
122
. The peak near 50 &mgr;sec in the diagram is a surge voltage caused by the induced electromotive force. Since the surge voltage will damage output transistor
105
and cause malfunction of other circuits, it is necessary to use a different diode outside inductive load driving circuit
101
to absorb the surge voltage. As a result, the cost will be increased, and it becomes difficult to miniaturize the circuit.
The objective of the present invention is to solve the aforementioned problems by providing an inductive load driving circuit that generates no surge voltage.
SUMMARY OF INVENTION
In order to realize the aforementioned objective, the present invention provides an inductive load driving circuit having a main transistor for supplying a current path to an inductive load, an auxiliary transistor that is connected in parallel with the aforementioned main transistor, and a control circuit, which has a first driver that supplies a first control signal to the control terminal of the aforementioned main transistor, a first wave shaping circuit that blunts the rising and falling characteristics of the aforementioned first control signal, a second driver that supplies a second control signal to the aforementioned auxiliary transistor, and a second wave shaping circuit that blunts the rising and falling characteristics of the aforementioned second control signal, and which can turn on/off both the aforementioned main transistor and auxiliary transistor.
In the inductive load driving circuit of the present invention, the aforementioned first wave shaping circuit has a first capacitor connected to the control terminal of the aforementioned main transistor, while the second wave shaping circuit has a second capacitor connected to the control terminal of the aforementioned auxiliary transistor.
Also, in the inductive load driving circuit of the present invention, the aforementioned first wave shaping circuit has a first resistor for restricting current to blunt the waveform of the aforementioned first control signal when turning off the aforementioned main transistor, and the aforementioned second wave shaping circuit has a second resistor for restricting current to blunt the waveform of the aforementioned second control signal when turning off the aforementioned auxiliary transistor.
In the inductive load driving circuit of the present invention, the aforementioned main transistor consists of an n-channel MOS transistor, while the aforementioned auxiliary transistor consists of a p-channel MOS transistor.
In addition, in the inductive load driving circuit of the present invention, the on/off timing of the aforementioned main transistor and auxiliary transistor are staggered.
In the aforementioned configuration, since the off timing of the auxiliary transistor is staggered, for example, delayed from the off timing of the main (output) transistor, the auxiliary transistor can release the energy remaining in the inductive load.
Also, when the source terminal of the auxiliary transistor is connected to the terminal where the counterelectromotive force of the inductive load occurs, even if a counterelectromotive force occurs in the inductive load when the output transistor is turned off, the magnitude of the counterelectromotive force can be clamped by the threshold voltage between the source terminal and gate terminal of the auxiliary transistor.
Also, the output transistor can be turned off slowly, and the current flowing to the output transistor is reduced gradually. After the current flowing to the inductive load is reduced to a level that will not cause a counterelectromotive force, the auxiliary transistor is turned off.
REFERENCES:
patent: 5699000 (1997-12-01), Ishikuri
patent: 5801550 (1998-09-01), Tanaka et al.
patent: 405304452 (1993-11-01), None
Brady III W. James
Kempler William H.
Le Dinh T.
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